Size-dependent variability of leaf and shoot hydraulic conductance in silver birch

Abstract

Variation in leaf and shoot hydraulic conductance was examined on detached shoots of silver birch (Betula pendula Roth), cut from the lower third (shade leaves) and upper third of the crown (sun leaves) of large trees growing in a natural temperate forest stand. Hydraulic conductances of whole shoots (K S ), leaf blades (K lb ), petioles (K P ) and branches (i.e. leafless stem; K B ) were determined by water perfusion using a high-pressure flow meter in quasi-steady state mode. The shoots were exposed to irradiance of photosynthetic photon flux density of 200-250 lmol m -2 s -1 , using different light sources. K lb depended significantly (P \ 0.001) on light quality, canopy position and leaf blade area (A L ). K lb increased from crown base to tree top, in parallel with vertical patterns of A L . However, the analysis of data on shade and sun leaves separately revealed an opposite trend: the bigger the A L the higher K lb . Leaf anatomical study of birch saplings revealed that this trend is attributable to enhanced vascular development with increasing leaf area. Hydraulic traits (K S , K B , K lb ) of sun shoots were well co-ordinated and more strongly correlated with characteristics of shoot size than those of shade shoots, reflecting their greater evaporative load and need for stricter adjustment of hydraulic capacity with shoot size. K S increased with increasing xylem crosssectional area to leaf area ratio (Huber value; P \ 0.01), suggesting a preferential investment in water-conducting tissue (sapwood) relative to transpiring tissue (leaves), and most likely contributing to the functional stability of the hydraulic system, essential for fast-growing pioneer species.

Developmentally based scaling of leaf venation architecture explains global ecological patterns

“…Thus, it would be possible to achieve higher final minor vein density in a smaller leaf by limiting leaf expansion after all veins are formed; or higher final minor vein density without change in leaf size by compensating with increasing expansion before the final vein order is formed; or higher final minor vein density with a larger leaf, with still greater expansion before the final vein order is formed; or a larger leaf without change in minor vein density by increasing expansion only before the final vein order is formed, thus initiating veins in the same proportion to leaf area as in the small leaf. All of these scenarios can occur, for example, for the sun relative to shade leaves of given species, and across populations or across closely related species adapted across habitats 4,12,[30][31][32][33][34][35][36][37] . Notably, leaf expansion relative to vein formation can be influenced by modulating cell proliferation, which especially affects expansion before the final vein order is formed, and final cell size, which mainly affects expansion after all veins are formed 38,39 .…”

Comparisons of stemflow yield and efficiency between two xerophytic shrubs: the effects of leaves and implications in drought tolerance

“…The positive effects could become negative if too many leaves enclose the branches, which would benefit throughfall instead. In general, factors such as a relatively large number of leaves (Li and Xiao, 2016), a large leaf area , a scale-like leaf arrangement (Owens et al, 2006), a small individual leaf area (Sellin et al, 2012) , a concave leaf shape (Xu et al, 2005), a densely veined leaf structure, an upward leaf orientation (Crockford and Richardson, 2000), leaf pubescence (Garcia-Estringana et al, 2010), and the leaf epidermis microrelief (e.g., the non-hydrophobic leaf surface and the grooves within it) (Roth-Nebelsick et al, 2012) together result in the retention of a large amount of precipitation in the canopy, supplying water for stemflow production, and providing a beneficial morphology that enables the leaves to function as a highly efficient natural water collecting and channelling system.…”

“…The answer may partly lie in the values of HV and PBMS. HV was computed as the cross-sectional area of the xylem divided by the total leaf area supported by the stems (Sellin et al, 2012). A higher HV indicates a potentially better water supply to leaves in terms of hydraulic conductance.…”

“…However, in terms of biotic mechanisms, although the canopy structure (Mauchamp and Janeau, 1993;Crockford and Richardson, 2000;Pypker et al, 2011) and branch architecture (Herwitz, 1987;Murakami 2009; (Herwitz, 1987;Murakami, 2009; Carlyle-Moses and Schooling, 2015) have been studied for years, the most important plant traits that vary with location and shrub species have not yet been determined. The effects of the leaves have been studied more recently at a smaller scale, e.g., leaf orientation (Crockford and Richardson, 2000), shape (Xu et al, 2005), arrangement pattern (Owens et al, 2006), pubescence (Garcia-Estringana et al, 2010), area (Sellin et al, 2012), epidermis microrelief (Roth-Nebelsick et al, 2012), amount (Li and Xiao, 2016), biomass (Yuan et al, 2016;Li et al, 2016), etc. Although comparisons of stemflow production during the foliated and dormant seasons usually indicate negative effects of leaves because the more stemflow occurred at the Hydrol.…”

Growth environment determines light sensitivity of shoot hydraulic conductance

“…The characteristics of the water relations of the upper foliage differ markedly from those of the lower foliage in canopy trees, e.g., leaf hydraulic (Sack et al 2003;Sellin et al 2011Sellin et al , 2012Nardini et al 2012) and stomatal (Eensalu et al 2008;Sellin et al 2010a) conductance are higher, but stomatal sensitivities to a decrease in leaf water potential (Sellin and Kupper 2005b; or in air humidity, to changes in light intensity (Sellin and Kupper 2005b), and to exogenous abscisic acid (Aasamaa et al 2004) are lower in top foliage shoots than in base foliage shoots. The light sensitivity of the stem hydraulic conductance of upper and lower foliage was compared by Sellin et al (2010b).…”